In order to stably light up while maintaining the brightness of the LED (light source) constant, it is necessary to drive the LED with constant current. For this purpose, a constant current source is used. LED drive circuit in Japanese Patent Application Publication No. 2013-157493 is provided with three constant current circuits for three LEDs connected in parallel to each other.
Further, for example, an LED board arranged at the front of the vehicle, an LED board arranged at the rear of the vehicle, and a constant current board are connected in series, and a plurality of LED boards is supplied with a drive current by one constant current board.
However, in the above-described LED drive circuit, the LED boards arranged in front and rear respectively, and the constant current circuit are set in separate housings, and are provided as separate parts. Therefore, there has been a problem that the number of parts increases. In recent years, in vehicles, the number of parts of the LED mounted tends to increase, further leading to increase of the number of parts.
Therefore, it is conceivable that the constant current board and one of the plurality of LED boards are mounted in the same housing to form one part. However, the LED has low heat resistant though the constant current circuit generates a large amount of heat, making it difficult to make them as one part as described above.